/**
 * Copyright 2005 The Apache Software Foundation
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.mapred;

import java.io.IOException;

/**
 * Protocol that task child process uses to contact its parent process.  The
 * parent is a daemon which which polls the central master for a new map or
 * reduce task and runs it as a child process.  All communication between child
 * and parent is via this protocol.
 */
interface TaskUmbilicalProtocol {

    /**
     * Called when a child task process starts, to get its task.
     */
    Task getTask(String taskid);

    /**
     * Report child's progress to parent.
     *
     * @param taskid   the id of the task
     * @param progress value between zero and one
     * @param state    description of task's current state
     */
    void progress(String taskid, float progress, String state);

    /**
     * Report error messages back to parent.  Calls should be sparing, since all
     * such messages are held in the job tracker.
     *
     * @param taskid the id of the task involved
     * @param trace  the text to report
     */
    void reportDiagnosticInfo(String taskid, String trace);

    /**
     * Periodically called by child to check if parent is still alive.
     */
    void ping(String taskid) throws IOException;

    /**
     * Report that the task is successfully completed.  Failure is assumed if
     * the task process exits without calling this.
     */
    void done(String taskid);

    /**
     * Report that the task encounted a local filesystem error.
     */
    void fsError(String message);

}
